The present invention generally relates to drilling methods for drilling a facing of a tunnel or the like to be excavated, in which a boom mounted with a drilling apparatus is positioned at predetermined drilling positions on the facing in accordance with a drilling pattern of the facing such that the facing is automatically drilled by the drilling apparatus. More particularly, the present invention relates to a drilling method for drilling an imaginary facing for curved excavation in the case of excavation of a curved tunnel, with the imaginary facing being angularly nonparallel to an existing facing.
Conventionally, it has been generally so arranged that when a tunnel or the like is excavated, drilling is performed in a fixed direction at a number of predetermined drilling positions of a facing of the tunnel such that explosives inserted into the drilled holes are blasted. To this end, a boom mounted with a drilling apparatus is required to be positioned at the predetermined drilling positions of the facing.
For positioning of the boom, a playback control method has been conventionally widely employed in which after a positioning operation (teaching operation) of the boom has been preliminarily performed so as to be stored, the teaching operation is played back. However, the known playback control method has such inconveniences that since the teaching operation is based on skill of an operator, its working efficiency is extremely low and its positioning accuracy is not satisfactory.
Thus, in place of the known playback control method, a numerical control method disclosed, for example, in Japanese Patent Publication No. 38752/1982 (Tokkosho No. 57-38752) has been recently employed. In the numerical control method, a drilling pattern expressed in a rectangular coordinate system defined with respect to a facing is transformed into a drilling pattern expressed in a coordinate system defined with respect to a drilling vehicle and then, on the basis of the latter drilling pattern, a boom mounted with a drilling apparatus is positioned at numerically designated predetermined drilling positions of the facing through feedback control such that the facing is automatically drilled. Meanwhile, in the case of excavation of a curved tunnel or the like, an imaginary facing (facing for curved excavation), which is vertically rearwardly retracted over a blasting penetration length from a new facing to be obtained by blasting at an existing facing, is nonparallel to the existing facing so as to form a predetermined angle therebetween. Thus, since the coordinate system defined with respect to the drilling vehicle is deviated from a coordinate system defined with respect to the facing for curved excavation, a deviation between coordinate systems defined with respect to the drilling vehicle and the facing for curved excavation, respectively is required to be modified. However, in the prior art numerical control method, since a deviation between a reference point in a coordinate system defined with respect to the existing facing and a reference point in the coordinate system defined with respect to the facing for curved excavation is measured merely in terms of angular deviations in vertical directions and the angular deviations are employed as a correction value, the deviation of the reference points does not necessarily coincide with the angular deviations when viewed on a plane, thus resulting in unsatisfactory positioning accuracy.